Studies of DNA hybridization for the fraction of DNA with repetition less than that represented by C sub o t equals 10 self renaturation has revealed a degree of nucleotide sequence diversity roughly parallel to phylogenetic relationships based on morphological and cytogenetic criteria. Confirmed sequence homology ranged from 38% between the repleta group (Drosophila mulleri and Hawaiian Drosophila (D. crucigera), to 74% between the Hawaiian Drosophila and the primitive subgenus Hirtodrosophila (D. duncanni). Karyotypic studies in the Hawaiian Drosophila are beginning to connect the genus Antopocerus with Drosphila, and some relationships between speciation and heterochromatin are being found in addition to the earlier findings in euchromatin by Carson, Stalker, Yoon, and others. A bioassay for carcinogens and teratogens seems to be emerging from these basic studies, and preliminary data are very promising.